PROJECT SUMMARY/ABSTRACT Spinal cord injury (SCI) is a devastating trauma that affects over 17,000 individuals in the United States per year, resulting in permanent paralysis for which there are no clinical therapies. These functional deficits are largely attributed to axon degeneration and extensive demyelination. Since surviving oligodendrocytes (OLs) cannot self-renew to remyelinate axons, the primary source of new myelin originates from proliferating NG2 progenitor cells. After SCI, it well-characterized that NG2 cells migrate and differentiate into new myelinating OLs along demyelinated axons. However, preliminary and published data suggest that NG2 cell differentiation and myelin biogenesis slow with advancing age. The frequency of SCI in the aging population is markedly increasing, yet the mechanism behind this impaired remyelination remains unknown. Here, we will use loss-of- function and gain-of-function experiments to investigate signaling pathways that contribute to the age- dependent decline in NG2 cell function, remyelination, and functional recovery after SCI. In particular, we will study two signals that regulate oligodendrogenesis: the mammalian target of rapamycin (mTOR) and glutamate. In Aim 1 we will genetically inhibit mTOR in aged mice to determine if mTOR downregulation reverses age-related impairments in CNS repair. Single cell RNA sequencing from young and aged mice will be run to further characterize changes in OL function and mTOR signaling. Then, in Aim 2 we will use viral vectors to test if overexpressing glutamate is sufficient to promote neuron-glia crosstalk and remyelination in aged-SCI mice. Collectively, these experiments aim to provide novel insight into how NG2 cells and myelination are regulated in the aging injured environment. If successful, data from this proposal will be one of the first to show that specific signaling molecules are responsible for anatomical and functional improvements in aged-SCI mice. This knowledge will aid in identifying new targets for therapeutic intervention to improve the quality of life of elderly SCI patients.